std::multiset::emplace(3)

💅 std::multiset::emplace

okay so bestie, welcome to the C++ Standard Libary page for std::multiset::emplace — like, yes, "Libary" is spelled that way in the header, we don't fix it, we just vibe 🫶. This is section 3 of the manual, and it's literally the glow-up of inserting stuff into a multiset.

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🌸 NAME 🌸

std::multiset::emplace — which is, and I cannot stress this enough, std::multiset::emplace 💀. The name is the name, bestie.

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✨ Synopsis ✨

template< class... Args >            (since C++11)
iterator emplace( Args&&... args );

So what's the tea? It inserts a new element into the container, constructed in-place with the given args. In-place. Right there. No travelling, no layovers 🧚.

The constructor of the new element is called with exactly the same arguments as supplied to emplace, forwarded via std::forward<Args>(args)....

Careful use of emplace allows the new element to be constructed while avoiding unnecessary copy or move operations. That's the whole point, that's the slay, that's the main character energy 👑.

No iterators or references are invalidated. NONE. Not one. Your iterators stay valid, your references stay valid, everyone's fine, we're all fine 🌈.

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🎀 Parameters 🎀

• args — arguments to forward to the constructor of the element. You hand them over, it forwards them, no questions asked.

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💖 Return value 💖

An iterator to the inserted element. That's it, that's the gift 🎁 — a little pointer to your brand new baby element.

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🔥 Exceptions 🔥

If an exception is thrown for any reason, this function has no effect (strong exception safety guarantee). Not a partial effect, not a "well, kind of" effect — literally no effect. It's giving all-or-nothing icon behaviour ⭐.

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⭐ Complexity ⭐

Logarithmic in the size of the container. Log. N. That's the whole vibe check.

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🦋 Example 🦋

// Run this code

#include <chrono>
#include <cstddef>
#include <functional>
#include <iomanip>
#include <iostream>
#include <string>
#include <set>

class Dew
{
private:
    int a, b, c;

public:
    Dew(int _a, int _b, int _c)
        : a(_a), b(_b), c(_c)
    {}

    bool operator<(const Dew& other) const
    {
        return (a < other.a) ||
               (a == other.a && b < other.b) ||
               (a == other.a && b == other.b && c < other.c);
    }
};

constexpr int nof_operations{101};

std::size_t set_emplace()
{
    std::multiset<Dew> set;
    for (int i = 0; i < nof_operations; ++i)
        for (int j = 0; j < nof_operations; ++j)
            for (int k = 0; k < nof_operations; ++k)
                set.emplace(i, j, k);

    return set.size();
}

std::size_t set_insert()
{
    std::multiset<Dew> set;
    for (int i = 0; i < nof_operations; ++i)
        for (int j = 0; j < nof_operations; ++j)
            for (int k = 0; k < nof_operations; ++k)
                set.insert(Dew(i, j, k));

    return set.size();
}

void time_it(std::function<int()> set_test, std::string what = "")
{
    const auto start = std::chrono::system_clock::now();
    const auto the_size = set_test();
    const auto stop = std::chrono::system_clock::now();
    const std::chrono::duration<double, std::milli> time = stop - start;
    if (!what.empty() && the_size)
        std::cout << std::fixed << std::setprecision(2)
                  << time << " for " << what << '\n';
}

int main()
{
    time_it(set_insert, "cache warming...");
    time_it(set_insert, "insert");
    time_it(set_insert, "insert");
    time_it(set_emplace, "emplace");
    time_it(set_emplace, "emplace");
}

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🍓 Possible output 🍓

499.61ms for cache warming...
447.89ms for insert
436.77ms for insert
430.62ms for emplace
428.61ms for emplace

(notice how emplace is lowkey just a lil faster — that's the whole point of the page, no cap 🙈)

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💜 See also 💜

• emplace_hint — constructs elements in-place using a hint (C++11) (public member function)
• insert — inserts elements or nodes (since C++17) (public member function)

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and that's the page, bestie!! 🎀 source is http://cppreference.com, dated 2024.06.10, and it's the std::multiset::emplace(3) manual page — periodt. go forth and emplace responsibly 💅✨